Venki Ramakrishnan

So there's a direct lineage all the way back to a few billion years that did not die. And so the germline, there is a chapter in my book which is called, I think, the immortal germline and the disposable body or soma. And so that is really a dichotomy in complex organisms. And in a way that's different from say bacteria or other organisms.

So there's a direct lineage all the way back to a few billion years that did not die. And so the germline, there is a chapter in my book which is called, I think, the immortal germline and the disposable body or soma. And so that is really a dichotomy in complex organisms. And in a way that's different from say bacteria or other organisms.

And what is interesting is that germlines aren't actually immortal, but we've evolved so that germlines are much better protected. For example, DNA damage or other kinds of damage are cause of aging. And germlines are protected much better against DNA damage and other kinds of damage. The other thing that happens is that germlines are selected almost ruthlessly.

And what is interesting is that germlines aren't actually immortal, but we've evolved so that germlines are much better protected. For example, DNA damage or other kinds of damage are cause of aging. And germlines are protected much better against DNA damage and other kinds of damage. The other thing that happens is that germlines are selected almost ruthlessly.

For example, when a female fetus, in the early embryonic stages, there are almost a million eggs or so. But of course, you know, you don't have, those million eggs are not, you don't have a million ovulation cycles. You know, in a human woman's life, maybe a few hundred eggs are, you know, secreted during menstruation, I mean, during ovulation. So what happens to all the others?

For example, when a female fetus, in the early embryonic stages, there are almost a million eggs or so. But of course, you know, you don't have, those million eggs are not, you don't have a million ovulation cycles. You know, in a human woman's life, maybe a few hundred eggs are, you know, secreted during menstruation, I mean, during ovulation. So what happens to all the others?

Well, the others are all ruthlessly selected because There's a whole process of selection from the oocyte, the precursor of the egg, all the way to the final egg that ends up ready for fertilization. And at each stage, it's monitored for defects and ruthlessly pruned out. And of course, sperm in males is also ruthlessly selected for, you know, millions of sperm and they all have to swim.

Well, the others are all ruthlessly selected because There's a whole process of selection from the oocyte, the precursor of the egg, all the way to the final egg that ends up ready for fertilization. And at each stage, it's monitored for defects and ruthlessly pruned out. And of course, sperm in males is also ruthlessly selected for, you know, millions of sperm and they all have to swim.

And if they can't make it and they are in any way defective, they just don't have a chance to undergo fertilization. And even after the embryo is formed, many embryos spontaneously abort without the mother even being aware of it in many cases. Some cases they are aware if it's later and there's a miscarriage. And so there's ruthless selection there.

And if they can't make it and they are in any way defective, they just don't have a chance to undergo fertilization. And even after the embryo is formed, many embryos spontaneously abort without the mother even being aware of it in many cases. Some cases they are aware if it's later and there's a miscarriage. And so there's ruthless selection there.

And even within the developing embryo, defective cells are destroyed. So I think this... I thought about why is it that we get old, but when a child is born, it's not born old. So it's as if the biological clock has been reset every generation. And that's because of this combination of protection and against damage for the germ cells and ruthless selection.

And even within the developing embryo, defective cells are destroyed. So I think this... I thought about why is it that we get old, but when a child is born, it's not born old. So it's as if the biological clock has been reset every generation. And that's because of this combination of protection and against damage for the germ cells and ruthless selection.

I think it's that combination that allows us to have an embryo that is, you know, looks, you know, it's gone back to state zero. But of course, all of the little tags on the DNA have been erased. These tags are markers for aging. They've been erased and and then reprogrammed to start from scratch.

I think it's that combination that allows us to have an embryo that is, you know, looks, you know, it's gone back to state zero. But of course, all of the little tags on the DNA have been erased. These tags are markers for aging. They've been erased and and then reprogrammed to start from scratch.

So so it's all this combination of things that goes on to to reset the the biological clock every generation.

So so it's all this combination of things that goes on to to reset the the biological clock every generation.

Yeah, so this has to do, you know, we talked about how some species live only a day or two and others live several hundred years. Well, you know, Jeffrey West, who we both know from Santa Fe, has written a great book called Scale. And in that book, he talks about relationship between lifespan and parameters like size.

Yeah, so this has to do, you know, we talked about how some species live only a day or two and others live several hundred years. Well, you know, Jeffrey West, who we both know from Santa Fe, has written a great book called Scale. And in that book, he talks about relationship between lifespan and parameters like size.

It turns out that large mammals live, on average, much longer than small mammals. Now, why would that be? Well, it's because evolution simply doesn't care how long you live. It cares about fitness, which is how likely are you to pass on your genes? How successful are you going to be at passing on your genes? And so I think...

It turns out that large mammals live, on average, much longer than small mammals. Now, why would that be? Well, it's because evolution simply doesn't care how long you live. It cares about fitness, which is how likely are you to pass on your genes? How successful are you going to be at passing on your genes? And so I think...